The present invention relates to data access mechanisms in high performance computers, and has particular relation to such mechanisms which do their work without lengthening the instruction word which invokes them.
A central processing unit (CPU) needs to know how to proceed through an associated memory: use every address, use only a portion of an address and concatenate, skip a certain number of addresses under certain conditions, etc. It also needs to know the type of number it is dealing with: signed, unsigned, fixed point, floating point, etc. These pieces of needed information are called the context in which the memory is being processed. If very long lines of software can be tolerated, the context can be specified anew in each line, allowing great flexibility. If strict limitations on context changing are imposed, software code lines may be made quite short, allowing great simplicity of operation. It has not yet been possible to do both.